This invention relates to an apparatus for recording and reproducing a digital signal, and more particularly to an apparatus for recording and reproducing a digital signal which is so adapted that, when an input digital signal is recorded onto a recording medium and is reproduced therefrom, reproduction is permitted with the apparatus with which the input digital signal was recorded, but reproduction is impossible with a recording and reproducing apparatus or a reproducing apparatus except for the above recorded apparatus.
In a DAT (Digital Audio Tape Recorder) using a rotary head among DATs capable of recording pulse code modulated sound data, obtained by applying pulse code modulation (PCM) to an analog audio signal, on a magnetic tape and reproducing the PCM sound data therefrom, a magnetization pattern to be recorded on the magnetic tape is recorded with azimuth angles of adjacent tracks being different from each other and with guard bands between tracks being absent. In such a DAT, subcodes are recorded on a track portion a fixed period from the initial end of each track and on a track portion a fixed period immediately before the terminating end thereof, respectively, and PCM signal data are recorded on the track intermediate portion except for the above-noted track portions in accordance with a predetermined format. The data thus recorded are reproduced.
CDs (Compact Disks) on which PCM sound data (digital signals) are recorded have been widely used. When the PCM sound data reproduced from the CD is recorded onto a magnetic tape with it being in the form of the digital signal, by means of, e.g., the above-mentioned DAT using a rotary head, high quality sound free from degradation of the sound quality can be recorded.
Meanwhile, where information (software) such as music recorded on CDs are recorded onto the magnetic tape, such a recording is permitted in accordance with the requirement of the Copyright Law only in connection with the case where individuals enjoy recorded information. On the other hand, when information (digital signals) recorded on CDs are recorded onto the magnetic tape in the form of a digital signal by means of DAT as stated above (which is so called a "digital copy" hereinafter), high quality sound free from degradation of the sound quality can be recorded. Accordingly, a large number of magnetic tapes digitally copied from a CD may be obtained. This is becoming a large problem from a viewpoint of the Copyright Law.
Thus, a copy guard system for preventing a large number of magnetic tapes from being digitally copied from CDs is highly desirable.